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paulfr
#1
Nov15-12, 12:29 AM
P: 179
How high can one suck water up a straw ?
Is this analysis and calculation correct ?
================
Straw sucking height limit calculation
Sucking up thru a straw from a height ...limit h = ? m

If the pressure P [=F/A] , the work done to lift the water column to h is
W = F dot s = PA x h/2 [average height = h/2]

The potential energy of the column is PE = ρAhg (h/2) [c of m is in the middle].
When the column rises up to its highest, there is no motion,
so all the energy is potential.
Equating work done to potential energy due to energy conservation

PAh/2 = ρAhg (h/2)
P = ρhg
h = P / ρ g
h = 1.0e5 N/m^2 / (1000 kg/m^3) ( 10 m/s^2)
h = 10 meters

Does that look correct ?

Thanks for your comments
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